This master should be used by designers working on Port of Portland construction projects and by designers working for PDX
tenants (“Tenants”). Usage notes highlight a few specific editing choices, however the entire section should be evaluated and
edited to fit specific project needs.
SECTION 260543 - UNDERGROUND DUCTS AND RACEWAYS FOR ELECTRICAL SYSTEMS
PART 1 - GENERAL
1.1
DESCRIPTION
A.
1.2
This section describes conduit, ducts, duct accessories, handholes, boxes and manholes
constructed and installed to form a complete underground raceway system.
RELATED WORK SPECIFIED ELSEWHERE
A.
Section 033000, Cast-In-Place Concrete
B.
Section 312300, Trenching, Backfilling, and Compacting
C.
Section 312319, Dewatering
1.3
REFERENCES
A.
AASHTO: American Association of State Highway and Transportation Officials
1.
AASHTO Specification for Highway Bridges
B.
ACI: American Concrete Institute
1.
ACI 318: Building Code Requirements for Structural Concrete and Commentary
C.
ASTM: American Society for Testing and Materials
1.
ASTM A48: Standard Specification for Gray Iron Castings
2.
ASTM C478: Standard Specification for Precast Reinforced Concrete Manhole Sections
D.
NEC: National Electrical Code
E.
UL: Underwriters Laboratories
1.
UL 651: Standard for Schedule 40, 80, Type EB and A Rigid PVC Conduit and Fittings
1.4
SUBMITTALS
A.
Submit product data and cut sheets.
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PART 2 - PRODUCTS
2.1
PRECAST HANDHOLES AND PULL BOXES
A.
Handholes and pull boxes are defined as boxes up to a size of 17"x30".
B.
The box shall be constructed from precast concrete or polymer concrete with an open bottom
unless noted otherwise on the drawings.
C.
The box shall be rated for incidental traffic. It shall be suitable for H-20 loading in off-street
locations that are not subject to high density traffic.
D.
The cover shall be engraved to indicate the contents such as “ELECTRIC,” “COMM,”
“LIGHTING,” “SIGNALS,” or as noted on the drawings.
E.
The cover shall be a non-skid surface, include lift or pull slots, and be capable of being secured
to the body with fasteners.
F.
The manufacturer’s name and model number shall be permanently indicated to an interior wall
face.
G.
Acceptable Manufacturers: Oldcastle, Christy, Hanson, Hubbell, or equal.
2.2
PRECAST CONCRETE VAULTS
A.
Vaults are defined as boxes larger than 17"x30".
B.
Vaults shall be precast concrete, solid bottom with a knocked out sump to allow for drainage,
embedded galvanized channels in each wall, a 1-inch diameter ground rod knockout in the floor,
and galvanized pull/lift irons in each corner. Vaults shall have an opening in the bottom to
allow drainage.
C.
Vaults shall be constructed from concrete that has a minimum 4,000 psi strength at 28 days.
D.
Design:
1.
Tops and walls of structures shall be designed for AASHTO H-20 highway loading, with
30 percent loading added for impact.
2.
Precast structures shall be designed in accordance with AASHTO Specification for
Highway Bridges. Concrete and reinforcing shall be designed in accordance with ACI
Code 318. Precast units shall conform to ASTM C478.
3.
Walls shall be designed to withstand all soil pressures, taking into consideration the soil
to be encountered and groundwater level present at the site. Assume ground water level
is at ground surface unless a lower water table is indicated in the boring logs.
4.
Precast vaults shall be designed and constructed not to float.
5.
Assembled sections shall have mating edges with tongue-and-groove joints. Joints shall
be designed to firmly interlock adjoining components, and provide waterproof junctions.
Joints shall be sealed watertight using preformed plastic strips installed in accordance
with the manufacturer’s instructions.
6.
Floor shall slope 2 percent in all directions to the sump.
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7.
8.
Steel components other than reinforced steel shall be hot-dip galvanized after fabrication.
Vaults shall be identified with manufacturer’s name embedded in, or otherwise
permanently attached to, an interior wall face.
E.
Vaults located in roadways shall be provided with round high density H-20 rated traffic covers.
Other areas such as sidewalks, parking lots, and landscape areas shall be provided with
galvanized steel hatches unless otherwise noted on the drawings.
1.
High density traffic areas shall be provided with H-20 rated cast iron manhole covers.
These covers shall be a minimum of 30-inch diameter, with lift holes and provisions to
secure into the vault top with fasteners. Round vault covers and frames shall be Class
30B grey cast iron in accordance with ASTM A48.
2.
Sidewalks, parking lots, and landscape areas shall be provided with traffic rated
galvanized steel hatches unless noted otherwise on the drawings. These covers shall
include a locking latch, a recessed lift handle, and a hinging system that allows the cover
to open a full 180 degrees. Communication vaults containing fiber optic back bone
cables shall be provided with a pad-lock compartment in the cover.
F.
All vaults shall be permanently labeled with the Port-assigned vault number. Vault designations
shall be visible from the surface. Communication vaults will be designated “CVLT-xxxx” and
electrical vaults designated “EVLT-xxxx,” where xxxx is a vault number assigned by the Port.
Cast covers shall have the designation cast into the cover at the casting foundry. If casting the
designation into the cover is not an option, the Contractor shall propose other means to
permanently label the vault. Galvanized steel hatches shall include the bead welded designation
onto the cover. If the cover cannot be bead welded, the Contractor shall propose other
permanent marking options.
G.
Conduit entries through vertical vault walls shall be through cast-in-place molded plastic duct
connections such as Term-A-Ducts unless otherwise noted on the drawings.
H.
Acceptable Manufacturers: Oldcastle, Hanson, or equal.
2.3
DUCT LINES
A.
Size: Except where otherwise shown on the drawings, ducts and conduits shall not be less than
4-inch trade size.
B.
Ducts (Concrete-Encased): Type II PVC Schedule 40, suitable for use with 90°C rated wire.
Conduit shall conform to UL Standard 651 and carry appropriate UL listing for below-ground
use.
C.
Ducts (Direct-Buried):
1.
Rigid Non-Metallic Conduit: Type II PVC Schedule 40, suitable for use with 90°C rated
wire. Conduit shall conform to UL Standard 651 and carry appropriate UL listing for
above- and below-ground use.
2.
Rigid Metal Conduit: UL 6 galvanized rigid steel. Where metal conduit is shown on the
drawings or specified below, conduit shall have a coating of 20 mil bonded PVC, or shall
be coated with bituminous asphaltic compound.
D.
Manufactured bends shall be not less than 36 inches in radius for conduits 4 inches in diameter
or larger. Fiberglass manufactured bends are acceptable.
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2.4
INNERDUCT
A.
2.5
Fabric duct type innerduct shall be constructed from flexible textile material and identified by
color-coded stitching for identification of cells. The fabric duct shall be pre-lubricated for
lower friction during innerduct and cable installation. All cells shall contain a color-coded pull
tape printed with sequential footage markings that has a minimum tensile strength of 1,250
pounds. The fabric duct shall be sized to match the raceway as 2-inch, 3-inch, or 4-inch
products and shall be three-way multi-cell unless noted otherwise on the drawings. The
material shall be resistant to ground chemicals and petroleum products and shall be unaffected
by mud, silt, or debris after installation. The number of cells in each conduit shall be as shown
on the drawings. The fabric duct shall be MaxCell Innerduct, or equal.
SPACERS
A.
2.6
Factory-fabricated rigid PVC vertical and horizontal interlocking spacers, sized for type and
sizes of ducts with which used, and selected to provide minimum of 3 inches separation
between ducts while supporting ducts during concreting or backfilling.
Acceptable
manufacturers: Carlon, Orangeberg, or equal.
GROUND RODS
A.
2.7
Ground rods shall be copper-clad steel, 3/4-inch diameter, and 10 feet long.
GROUND WIRE
A.
2.8
Ground wire shall be stranded bare copper No. 6 AWG minimum.
CONDUIT EXPANSION/DEFLECTION FITTINGS
A.
Conduit expansion/deflection fittings in embedded runs shall be rated for indoor use, outdoor
use, buried underground, or embedded in concrete in non-hazardous areas.
B.
Fittings shall allow axial expansion or contraction up to 3/4 inch and angular misalignment of
the axes of the coupled runs in any direction to 30 degrees. Inner sleeves shall maintain
constant inside diameter in any position and provide smooth insulated wireway for protection of
wire insulation.
C.
Fittings shall have a watertight flexible neoprene outer jacket and tinned copper flexible braid
grounding strap.
D.
Use with galvanized rigid steel conduit or PVC Schedule 40 conduit utilizing rigid metal
conduit nipples and rigid metal to PVC adapters.
E.
Acceptable Manufacturers: Crouse-Hinds, O-Z/Gedney, or equal.
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PART 3 - EXECUTION
3.1
CONDUIT ENCASEMENT OR EMBEDMENT (STRUCTURES AND DUCT BANKS)
A.
Concrete shall be class 3500-3/4 with red dye. Red dye may be installed onto the top of the
concrete encasement.
B.
Concrete-embedded conduit shall be separated from the earth by at least 3 inches of concrete.
Clearances shall be equal to the conduit diameter, but not less than 1 1/2 inches. Clearances
shall also be maintained between conduits encased in slabs. Clearances of less than 1 1/2 inches
at conduit crossing and terminating locations are acceptable.
C.
Provide conduit expansion/deflection fittings where embedded conduit crosses building
expansion joints, passes between two adjacent structures, or passes between a duct bank and
structure. Locate conduit expansion/deflection fittings between duct bank and manholes or pull
boxes where noted on the drawings.
D.
Place duct banks on an undisturbed soil base wherever possible. Where duct banks pass
through backfilled areas, the soil base shall be as specified elsewhere in the project manual.
Duct banks that run under traffic areas shall be steel reinforced.
E.
Locate plastic spacers 5 feet to 8 feet on center as recommended by the manufacturer. Tie
entire assembly together using fabric straps; do not use tie wires or reinforcing steel that may
form conductive or magnetic loops around ducts or duct groups. Secure spacers to earth and to
ducts to prevent conduit flotation during concreting. Conduit runs shall be watertight.
F.
Protect conduit ends from damage during construction. When using plugs for protection, a
1/4-inch hole shall be drilled in the lower portion of the plug to provide drainage.
G.
Where a conduit is specified “spare” or for future use, install a nylon cord in conduit and fasten
at each end.
H.
Pull leather-washer-type duct cleaner, with graduated washer sizes through full lengths of ducts
immediately after concrete is poured. After the concrete has set but before backfilling, pull a
4-inch-long mandrel having a diameter equal to the conduit’s inside diameter minus 1/2 inch
through each conduit. The mandrel shall be lead-covered or painted white so that it will
indicate any protrusion on the inside of the conduit.
3.2
PRECAST HANDHOLES AND PULL BOXES INSTALLATION
A.
Install precast handholes and pull boxes on a solid ring of base material such as concrete around
the outer edge to prevent settlement. The base material shall include openings that allow
drainage from the box into the soil. Boxes shall be set plumb and elevated slightly above
surrounding grade to prevent them from becoming the water collection points. Conduit ends
shall be sealed to prevent debris from entering the raceway.
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3.3
PRECAST VAULTS INSTALLATION
A.
Locate vaults at the approximate location shown on the drawings with due consideration given
to other utilities, grades, duct lines, obstructions, and paving.
B.
Install on a level bed of well-tamped gravel or crushed stone, well-graded from the 1-inch to
2-inch sieve. Compact rock to prevent settlement, and then install drainage fabric over the area
where the vault sump will be located. The sump shall be a clear opening from the vault interior
to the surrounding surface to provide a pathway for water.
C.
In paved areas, set top of vault plumb and flush with finished surface. In unpaved areas, set
vault top slightly higher than surrounding area to prevent the vault from collecting surrounding
water.
D.
Install a ground rod in each vault through the ground rod knockout in the floor.
E.
Install a bonding conductor along the perimeter of the interior walls. Bond all metallic parts
including all embedded channels, frames, ladders, etc. Connect the ground rod to this bonding
conductor.
F.
In cases where Term-A-Ducts were not provided at conduit entries, fill the breakout windows
with concrete or non-shrink grout after all ducts have been installed. Conduit entries shall be
provided with a smooth bell end to prevent cable damage.
G.
Affix a laminated plastic label to the vault wall adjacent to each conduit entry/exit. The label
shall indicate the conduit number and its destination. For example, “#1 to CVLT-1234”
indicates that conduit #1 extends to vault CVLT-1234. Labels shall be engraved phenolic that is
suitable for the environment. Acceptable attachment methods include stainless steel fasteners
and permanent epoxy.
H.
Install a Port-furnished Confined Space Identification sign to the underside of the vault lid or
affix the sign to near the top of the vault wall with stainless steel screws.
3.4
TRENCHING
A.
Excavate trenches in accordance with Section 312300, Trenching, Backfilling, and Compacting.
B.
Work with extreme care near existing utilities to avoid damaging them. Cut the trenches neatly
and uniformly.
C.
For Concrete-Encased Ducts:
1.
After excavation of the trench, drive stakes in the bottom of the trench at 4-foot intervals
to establish the grade and route of the duct bank.
2.
Pitch the trenches uniformly toward manholes or both ways from high points between
manholes for the required duct line drainage. Avoid pitching the ducts towards buildings.
3.
The walls of the trench may be used to form the side walls of the duct bank provided that
the soil is self-supporting and that the concrete envelope can be poured without soil
inclusions. Use forms where the soil is not self-supporting.
4.
After the concrete-encased duct has sufficiently cured, backfill the trench in accordance
with Section 312300, Trenching, Backfilling, and Compacting.
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3.5
DUCT LINE INSTALLATIONS
A.
General:
1.
Duct line shall be in accordance with the NEC, as shown on the drawings, and as
specified.
2.
Slope duct to drain toward manholes and away from building and equipment entrances.
Pitch shall be not less than 4 inches in 100 feet. Curved sections in duct lines shall
consist of long sweep bends with a minimum radius of 50 feet in the horizontal and
vertical directions unless noted otherwise on the drawings. The use of manufactured
bends is limited to building entrances and stub-ups to equipment.
3.
Underground conduit stub-ups to equipment inside buildings shall be galvanized rigid
steel and shall extend at least 10 feet outside the building foundation. Stub-ups to
equipment, mounted on outdoor concrete slabs, shall be galvanized rigid steel and shall
extend at least 5 feet from edge of slab. Install insulated grounding bushings on the
terminations. Couple the steel conduits to the ducts with suitable adapters, and encase
with 3 inches of concrete.
4.
Upon completion of the duct bank installation, pull a standard flexible mandrel through
each duct. The mandrel shall be at least 12 inches long, and shall have a diameter
1/2 inch less than the inside diameter of the duct. After mandreling, pull a brush with
stiff bristles through each duct to remove the loosened particles. The diameter of the
brush shall be equal to or slightly larger than the diameter of the duct.
5.
Seal the ducts and conduits at building entrances and at outdoor equipment terminations
with a suitable non-hardening compound.
6.
Conduits shall be joined, terminated and sealed with fittings, materials and methods
recommended by the manufacturer. Supply all necessary fittings and materials for a
complete conduit/duct system.
B.
Concrete-Encased Ducts:
1.
Duct lines shall consist of single or multiple duct assemblies encased in concrete, and
installed with top of duct bank not less than 36 inches below established grade unless
otherwise indicated. Ducts shall be uniform in size and material throughout the
installation.
2.
Rigid base and intermediate spacers shall securely support and maintain uniform spacing
of the duct assembly at least 3 inches above the trench bottom during pouring of concrete.
Spacer spacing shall not exceed 8 feet. Use a minimum of 3 spacers for each 20-foot
length of duct.
3.
Clearances between individual ducts:
a.
For like service, clearance shall be not less than 3 inches.
b.
For high voltage power and telephone services, clearance shall be not less than
6 inches.
c.
For high voltage and 600 volt services, clearance shall be not less than 3 inches.
d.
Provide tie wires to prevent displacement of the ducts during pouring of concrete.
Tie wires shall not act as substitutes for spacers.
4.
Terminate duct lines at window openings in manhole walls as shown on the drawings.
Adjust window openings to correspond with duct line inverts. All ducts shall be fitted
with end bells.
5.
Couple the ducts in staggered rows and layers to ensure maximum strength and rigidity of
the duct bank.
6.
Extend the concrete envelope encasing the ducts at least 3 inches beyond the outside
walls of the outer ducts and conduits.
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7.
8.
9.
C.
3.6
Install reinforcing steel bars within the top and bottom of each concrete envelope within
5 feet of the building, at manhole wall penetrations, under roadways, and between
concrete pours. Where shown on the drawings, incorporate additional steel reinforcing in
the duct envelopes.
Keep ducts clean of earth, sand, or gravel during construction, and seal with tapered
plugs upon completion of each portion of the work.
Where new ducts, conduits, and concrete envelopes are to be joined to existing manholes,
make the joints with the proper fittings and fabricate the concrete envelopes to ensure
smooth, durable transitions.
Direct Burial Duct and Conduits:
1.
Install direct burial ducts and conduits only where shown on the drawings.
2.
Ducts and conduits shall be joined and terminated with fittings recommended by the
conduit manufacturer.
3.
Tops of ducts and conduits shall be not less than 24 inches below grade.
4.
Do not kink the ducts or conduits.
UTILITY WARNING TAPE AND LOCATE WIRE
A.
Place a continuous strip of utility warning tape approximately 12 inches above ducts or conduits
before backfilling trenches. See Section 312300, Trenching, Backfilling, and Compacting, for
tape description and installation requirements.
B.
Provide utility locate wire as described in Section 312300.
C.
Extend locate wire to near vault top and secure with an additional 2 feet of spare loop.
Additional conductor length allows equipment used by locators to be positioned outside the
vault, thereby eliminating a confined spare entry.
END OF SECTION 260543
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